With reference to FIGS. 1 and 2, a simple Boost converter 200 comprises a voltage source 21 having a first and second terminal (here one terminal+ground), an inductor 23 whose first terminal is connected to the +terminal of the voltage source 21, a diode 24 whose anode is connected to the second terminal of the inductor 23, a current switch 26 such as a MOSFET field effect transistor connected between the second terminal of the inductor 23 and the ground.
The functioning of the simple Boost converter 200 can be divided into two separate phases depending on the status of the switch 26: an energy accumulation phase (FIG. 1) and an energy transfer phase (FIG. 2). During the energy accumulation phase (FIG. 1), the switch 26 is closed (on-state), this leading to an increase in current in the inductor 23 and hence the storing of a quantity of energy in the form of magnetic energy. The diode 24 is then blocked and the load 27 is disconnected from the power supply. During the energy transfer phase (FIG. 2), the switch 26 is open, the inductor 23 then being in series with the generator and its electromotive force is added to that of the generator (booster effect). The current passing through the inductor then passes through the diode 24 and the load 27. As a result, a transfer occurs of the energy accumulated in the inductor 23 towards the load 27.
With reference to FIG. 3, to improve on the performance of a simple Boost converter regarding the rated voltage, a structure called an interleaved double BOOST converter 300 has been proposed. It is the combination of two simple Boost circuits having the mid-points of the switches 26 and filter capacitors 25 connected both to one another and to the terminals of the load 27 (FIG. 3), the controls of the switches being shifted by a half-period (see FIG. 4 which illustrates the status of the first switch at the top, the status of the second switch in the middle and underneath the inductor current).
One disadvantage of this type of converter is that its yield decreases with increases in operating frequency, whereas in contradiction it is preferable to choose high operating frequencies of the order of 100 kHz to 1 MHz, to reduce the size and volume of the converter. It is well known that a reduction in yield with an increase in operating frequency is notably caused by energy losses in the switches 24 and diodes 26 during the switching periods, such switching then commonly being called hard switching.
To overcome this shortcoming it has been proposed to add capacitors called snubber capacitors in parallel with the switches, which makes it possible to soften switching. The adding of these snubber capacitors allows solving of the problem of switching losses on opening of the switches, but does not allow solving of the problem of switching losses on closing of the switches. Since the snubber capacitors are charged on opening of a switch, they become discharged on closing thereby aggravating switching losses on closure of the switches.
Such switching leads to an energy loss that is all the more sensitive the higher the frequency. Additionally, the voltage front on closing of the switches translates as the emitting of parasitic electromagnetic radiation.